High intensity focused ultrasound (HIFU) is a medical technology capable of transcutaneous localized ablation of target sites without damaging intervening tissues. In most high intensity focused ultrasound applications, tissue is thermally ablated due to heating caused by ultrasound energy absorption. Various techniques exist for HIFU waves to ablate, damage, or disintegrate an object such as a diseased biological tissue or a foreign body within a patient. More specifically, energy carried by HIFU waves may be absorbed by a given portion of the object, so that the temperature of the given portion is increased, causing thermal ablation of the given portion. HIFU waves can also be sequentially focused (e.g., deflected or scanned) upon different portions of the object so that a larger macroscopic region of the object is thermally ablated. Conventional HIFU processes that primarily cause thermal ablation generally involve the use of HIFU waves with power densities of less than 1 kW/cm2.
An important aspect of HIFU therapy is imaging the treatment site for targeting the HIFU beam (treatment planning), monitoring the treatment in real time (treatment monitoring), controlling the location of targeted region as well as delivered dose to this region (treatment control), and evaluating the final therapeutic effect (post-treatment assessment). In particular, various forms of magnetic resonance imaging (MRI) and related MR diagnostic techniques can be used for this purpose.